Oh, I'm aware of that (thanks to Micheál Ó Siadhail's "Learning Irish"). It really is a harder part of Irish phonetics, though.
(I have no trouble distinguishing between broad and slender consonants, but to tell apart the two slender L's or N's is much more difficult.)

Actually it's easy when you hear people who pronounce them properly (which isn't the case of 99% of non-native speakers, ie. most of what you can hear on the web).
/l'/ is a "light l", very slightly palatalised but you do't hear a y-sound.
/L'/ is more or less like the "ly" sound in "million", I guess it's like Russian ль

/n'/ is a "light n", very slightly palatalised but you do't hear a y-sound.
/N'/ is more or less like the "ny" sound in "new" (in UK English - Americans pronounce it as "noo" as far as I know), I guess it's like Russian нь

These sounds are very different and you can't mix them up at all.
The ones that are harder to distinguish are the broad ones : /n/ vs /N/, /l/ vs /L/. But I think many people don't make a distinction between them any more...

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Is fearr Gaeilg na Gaeltaċta ná Gaeilg ar biṫ eile
Agus is í Gaeilg Ġaoṫ Doḃair is binne

I think "minion" is a word where "ny" sound is pronounced the same on both sides of the Atlantic Ocean. Most English speakers also are familiar with Spanish "señor".

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[hr]Múinteoir Gaeilge - Irish Teacher[/hr]
My "specialty" is Connemara Irish, particularly Cois Fhairrge dialect, but I can also speak Ulster and Munster Irish with native-level pronunciation.
Is fearr Gaeilge ḃriste ná Béarla cliste, cinnte, aċ i ḃfad níos fearr aríst í Gaeilge ḃinn ḃeo na nGaeltaċtaí.
Gaeilge Chonnacht (GC), go háraid Gaeilge Chois Fhairrge (GCF), Gaeilic Uladh (GU), Gaelainn na Mumhan (GM), agus Gaeilge an Chaighdeáin Oifigiúil (CO).